Quantum dot memory may be 'Holy Grail' of computing

时间：2019-03-02 09:15:03166网络整理admin

By Mason Inman Memory made from tiny islands of semiconductor – known as quantum dots – could fill a gap left by today’s computer memory, allowing storage that is fast as well as long lasting. Researchers have shown they can write information into quantum dot memory in just nanoseconds. Solid-state memory chips – as opposed to hard drives with moving parts – come in two forms. Computers use quick dynamic access memory, or DRAM, for short-term memory. But data does not persist for long and must be refreshed over 100 times per second to maintain its memory. Flash memory like that used in memory cards and smaller iPods is, despite its name, the elephant of solid memory. It can store data for years without refreshing, but writes information about 1000 times slower than DRAM. New research shows that memory based quantum dots can provide the best of both: long term storage with write speeds nearly as fast as DRAM. A tightly packed array of the tiny islands – each around 15 nanometers across – could store one terabyte (1000 gigabytes) of data per square inch, the researchers say. Dieter Bimberg and colleagues at the Technical University of Berlin, Germany, with collaborators at Istanbul University, Turkey, demonstrated it is possible to write information to the quantum dots in just 6 nanoseconds. “The very first prototype of the new quantum-dot-based memory is already as almost fast as a DRAM,” says study co-author Andreas Marent, also from the Technical University of Berlin. The researchers achieved the quickest write times with quantum dots made from a blend of two semiconductors, indium arsenide and gallium arsenide. Similar dots made with other materials were still very fast, at 14 nanoseconds. In flash memory, digital 1s and 0s of data are altered by shunting electrons in or out of an electrically isolated silicon electrode. But those processes have to overcome an “energy barrier” – a relatively slow process that gradually degrades a memory chip’s quality and significantly limits its lifespan. Quantum dots work in a similar manner – storing data involves shunting a dot’s electrons into a different energy band. But quantum dot memory is faster and more robust because an electric field can be used to temporarily lower the energy barrier. Quantum dots have potential to go even faster still, says Marent. “In contrast to DRAM or Flash, the physical limit of the write time for quantum dots is in the picosecond range,” he says. “That means a better device prototype should be more than 100 times faster than today’s DRAM.” This first demonstration of ultra-fast writing to quantum dots, “suggests that quantum dots may be more useful for memory than researchers had thought,” says Aimin Song of the University of Manchester, UK. Because ever large amounts of data are being stored and retrieved “the writing time has been rapidly becoming a limiting factor with conventional memories,” Song told New Scientist. “So this work may stimulate a lot of interest from the [computing] industry. A device that could bridge the gap between DRAM and flash is “the ‘Holy Grail’ of memories,” says Claes Thelander of Lund University in Sweden. Although other memory designs being investigated, quantum dots are a promising approach, he adds. Journal reference: Applied Physics Letters (DOI: 10.1063/1.2890731) Nanotechnology – Follow the emergence of a new technology in our continuously updated special report. More on these topics: